The present invention relates to solid-state imaging device and to a solid-state imaging system using the solid-state imaging device, and more particularly relates to a noise correction of an output of solid-state imaging device.
It is known in those solid-state imaging devices used for example in video camera that pattern noises occur due to its various factors. One of the pattern noises is a stripe-like pattern noise in a vertical or horizontal direction which occurs due to variance among circuits disposed in row or column direction, and another is an unevenness pattern noise due to variance in pixel characteristics such as the variance in dark current that occurs in each pixel. These are referred to as a fixed pattern noise, since the location where these noises occur is fixed.
Further, a pattern noise depending on the luminance and/or shape of object is also known as pattern noise. For example, when image is taken of an object having a highlight pattern as shown in FIG. 1A, a band-like pattern noise “b” on the left and right sides of the highlight pattern “a” as shown in FIG. 1B may occur in the image signals obtained from solid-state imaging device. This band-like pattern noise “b” occurs for example such that a circuit section provided within the solid-state imaging device for reading pixel signals and/or bias inputted from the outside for example are affected by fluctuation of signal level in the highlight pattern “a”. The band-like pattern noise “b” appears on an image signal as if an offset is superimposed on the image signal. Further, the image may appear in an outwardly extended manner about the highlight pattern “a” due to diffusion of electric charge within the semiconductor substrate which forms the solid-state imaging device.
As a method for correcting these noises, it has been known to use a circuit as shown in FIG. 2 as disclosed for example in Japanese Patent Application Laid-Open 2002-125155. This method is performed as in the following. In particular in FIG. 2, when a shutter button (not shown) is turned ON, a light-shielding plate 31 is opened through a driver 40 by control signal from a system controller 42. An object image is thereby formed on an imaging plane of a CCD 32 by an optical system (not shown) provided at a front stage of the light-shielding plate 31, and such object image is photoelectrically converted by the CCD 32 which is driven by a driver 41. Thus obtained imaging signals are A/D-converted at an A/D converter 33 and then accumulated at a frame memory 34 as image signals.
Next, a photoelectric conversion is effected by the CCD 32 in a dark condition where the light-shielding plate 31 is closed. Since thus obtained imaging signals are obtained by photoelectric conversion effected in a condition where light from the outside onto the CCD 32 is completely cut off, these are used as noise component data SN of a fixed pattern noise of the CCD 32.
Thus obtained noise component data SN are directly inputted to one end of a subtractor 36 without being subjected to such processing as A/D conversion by the A/D converter 33. In synchronization with the inputting of the noise component data SN into the subtractor 36, then, the image signals of object accumulated at the frame memory 34 are D/A-converted at a D/A converter 35 and are inputted to the other end of the subtractor 36 as analog image signals SD. A subtraction processing, i.e. SD-SN is then conducted at the subtractor 36 so that a correction signal S from which noise components of CCD 32 are removed is obtained. The correction signal S is subjected to a predetermined processing at a process circuit 38 and then given to a recording apparatus 39 so as to be recorded. In other words, the method using the circuit of FIG. 2 is to generate a light-shielded image signal at each image taking by providing a means for cutting off the light from the object to the imaging device, and to provide an output by subtracting the image signal at the time of cutting off the light from the image signal of the main photographing where the light is allowed to be incident. It should be noted that what is denoted by numeral 37 in FIG. 2 is a switch for outputting the correction signal S or uncorrected signal in a switching manner.
Further, there is a known solid-state imaging device as shown in FIG. 3 which is disclosed in Japanese Patent Application Laid-Open 2007-19820. FIG. 3 shows the construction of a pixel section of the solid-state imaging device disclosed in the publication, where 501 and 502 denote an effective pixel region and a light-shielded region (0B region), respectively. The light-shielded pixels denoted by 503 are then scattered within the effective region 501. By disposing the light-shielded pixels 503 within the effective pixel region 501 in this manner, a black level of the effective pixel region 501 as a whole can be grasped. An unevenness pattern noise due to variance in dark current can thus be corrected with using the light-shielded pixels 503 provided within the effective pixel region 501.